Integrate meta-seco-edgehog/kirkstone/develop_sign_key

Commit: https://git.seco.com/yocto_ng/layers/seco/meta-seco-edgehog/-/commit/4831fa468f57f377b96c0c48ea3f587657009fe8

[rauc][cert] Moved the example cert/key to the insecure-keys folder

Moved the example cert/key to a new folder called insecure-keys to further emphasise that they must not be used in production environments.

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Commit: https://git.seco.com/yocto_ng/layers/seco/meta-seco-edgehog/-/commit/ea6052de688e27296072b06469e964ecedafc0bc

[rauc][cert] Enabled install of custom keyring for RAUC

If a user creates custom RAUC bundles, we also need to include the cert as keyring into the image. The keyring file is used to verify future releases when updating via OTA.

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Commit: https://git.seco.com/yocto_ng/layers/seco/meta-seco-edgehog/-/commit/71bd4a5c1b218c746835009110cda7920ae8bc02

[rauc][signing] Enabled custom RAUC key/cert

The user can now set a custom key and cert for the signing of RAUC bundles.